Fluid bed granulation is being used increasingly in the pharmaceutical, food and chemical industries because of its special agglomeration capabilities. The pharmaceutical industry has been using fluid bed technology for more than ten years in the development and production of solid dosage forms.
A fluid bed granulator usually consists of a filter chamber, expansion chamber with one or more spray nozzles, product bowl and air inlet plenum. A fluid bed granulator operates by fluidizing a particulate material with air supplied from the air inlet plenum. Simultaneously a binding solution is sprayed onto the fluidized particulate material to facilitate the aggregation of individual particles into larger granules. The wet aggregates are dried by the fluidizing air in the granulator. The process is continued until the granules achieve the desired size.
During the granulation process, the moisture content of the granules should be monitored carefully. The moisture content is directly related to particle size, uniformity of the size distribution and build-up rate of the granules produced during the granulation process. Currently the moisture content of granules is monitored manually. The operator takes samples from the granulator at regular intervals and determines the loss of weight on drying the sample (LOD). The loss of weight is then correlated to the moisture content of the granules. The LOD test takes from 5-15 minutes to be performed depending on the product moisture. The operator will then analyze the moisture data and adjust the operating parameters accordingly. Since the LOD test is time consuming, the number of LOD tests that can be performed during granulation is limited. In addition there is always the inherent sampling error because of differing sample size and sample non-uniformity. The error prone and delayed information from the LOD test causes the granulation process to produce inconsistent and out of specification product on a regular basis.
Recently infrared and near infrared moisture analyzers have begun to replace the LOD test as the preferred method of determining moisture content. Although, using infrared and near infrared analyzers to measure the moisture content of samples significantly reduces the time delay in measuring the moisture content it does not eliminate sampling errors. Special precautions must be taken with infrared and near infrared moisture analyzers. Since these analyzers measure only surface moisture exposing samples to ambient conditions will result in significant errors in the measurement made by infrared or near infrared analyzers. As a solution to this problem, it has been suggested to locate an infrared or near infrared moisture sensor within the fluid bed granulator to provide on-line moisture content data.
However, the environment within a fluid bed granulator makes it very difficult to obtain accurate measurements of the moisture content with an infrared or near infrared moisture analyzer. If the sensor is placed flush with the wall of the product bowl a cake of noncirculating particulate material will block the infrared sensor. If the sensor is further into the product bowl, the turbulent flow of fluidizing air and particulate material will not have the necessary constant bulk density to provide a reliable reading.
Thus it would be a significant contribution to the art to provide a process and apparatus for facilitating the accurate measurement of the moisture content of the particulate material within a fluid bed apparatus. It would also be a significant advancement to the art to provide an apparatus and process which would allow for the moisture content of the particulate material of a fluid bed apparatus to be monitored and operating variables of the fluid bed apparatus to be adjusted in response thereto.
One object of the present invention is to provide an apparatus and process for monitoring the moisture content of the particulate material in a fluid bed apparatus.
Another object of the present invention is to provide an apparatus and process for monitoring the moisture content of the particulate material in a fluid bed apparatus and automatically adjusting operating variables in response thereto.
A further object of the present invention is to provide a near infrared probe suitable for use in a fluid bed apparatus.
These objects and other objects and several advantages provided by the present invention are presented in the following specification including the Figures, Examples and claims.